It is often necessary, for reasons well known to those in the drilling art, to control the course of a progressing well bore being drilled. In the past, unwanted deviation from vertical was of prime concern. More recently, well bores were directionally drilled when necessity dictated, to drill into otherwise inaccessible formations. With more sophisticated equipment, directional drilling is now practiced for convenience as well as economy.
For well bore deflection purposes, bending the drill string about a transverse axis fixed to the drill string can be done with rugged and reliable machinery. The related drilling practice generally requires a drilling motor below the bend or a lateral jet in the drill head. The drill string bend can be permanent in the form of a "bent sub" but that system is not considered suitable for straight hole drilling. Once a well bore is deflected from an original path, the "reach" of hole subsequently drilled usually does not require continued deflecting effort. The drill string is conventionally tripped from the hole to remove the bent sub until the next time deflection is needed.
There has been a recognized need for some time for the ability to change the downhole assembly from a directional configuration to a straight hole drilling configuration, and ideally to reverse the process, without tripping the drill string. This need has produced "knuckle joint" tools that have hinge means to accomplish the effect of a bent sub. The ideal objective of commanding the sub to accomplish the bent result by simple manipulation of drilling controls at the surface has received some effort, with some success, in recent years, and this invention is an effort to further that art. In the drilling arts, simplicity generally results in greater reliability and this invention is directed to a deflection tool of simple construction and simple controls.
It is an object of this invention to provide a drill string deflection tool that can be controlled by manipulation of the drilling controls at the surface to provide a straight drilling or a deflected drilling configuration of the downhole assembly. It is a further object to cause the change in configuration by axial manipulation of the drill string and to lock in the selected configuration by manipulation of drilling fluid flow controls.
It is another object of this invention to provide a downhole drill string deflection apparatus that can influence the resistance to the flow of drilling fluid such that the configuration of the downhole assembly will be indicated at the surface by the pressure-flow relationship of the drilling fluid circuit.